This invention relates to a numerical control unit for numerically controlling an industrial machine and, more particularly, to a programmable numerical control unit which is capable of on-site creation and entry of a machining program.
Generally, a numerical control unit (referred to as a NC unit) of the kind that finds wide use in the art is adapted to create an NC tape containing a machining program, and to read the tape by means of a tape reader mounted on the NC unit to enter the machining program. NC units also include so-called manual NC units which are simple in construction and make no use whatsoever of a tape reader. In a manual NC unit, positioning or cutting data is preset on a number of dials mounted on the panel of the NC unit which, subsequently, reads the positioning or cutting data from the dials in successive fashion to execute numerical control processing. Alternatively, numerical data may be entered successively from an MDI (manual data input device) and stored in memory, after which the NC unit reads out the numerical data successively to perform numerical control processing. Thus, a manual NC unit is characterized in that (1) direct programming is performed at the job site while the programmer observes his machining drawing, (2) the program data is entered by means of the dials or MDI, and (3) the machine tool is made to perform an actual machining operation based on this data.
In such conventional manual NC units, however, programming is extremely difficult, machining efficiency is poor because of the considerable time required for programming, and input errors are common. Though manual NC units have been proposed which enable easy programming from machining drawings in a shorter period of time and with fewer errors, these proposed manual NC units are not always fully effective in shortening the time required for programming, even though the time required is less than in the prior art. In addition, control of machining performed by a machine tool cannot be carried out while programming is in progress. A serious disadvantage even with these proposed manual NC units, therefore, is that machining efficiency is poor.
Furthermore, since a manual NC unit does not, by nature, possess such data input/output equipment as a tape reader/puncher and bubble memory cassette there is no way to preserve for possible future use a machining program created through painstaking effort, and no way to enter NC program data from an external storage medium. Thus, an NC unit of this type is inefficient since NC data must be created with each use, even though the identical machining operation may be performed at some future date.